Once other conditions, such as depression, Huntington’s disease or hypothyroidism, have been ruled out, an Alzheimer’s diagnosis is made by accumulating information on the individual’s history and mental status exams and by interviews with the patient, family members and friends over a period of several weeks. Diagnoses based on this type of clinical information are accurate about 90 percent of the time.
In 2011 the National Institute on Aging-Alzheimer’s Association workgroup published new guidelines for diagnosing Alzheimer’s disease. The criteria are designed to be used by both primary care doctors (who would not have access to neuropsychological testing and advanced imaging equipment) and specialists.
In order to be diagnosed with probable Alzheimer’s dementia, a person has to meet the criteria for dementia and have the following qualities:
- Symptoms have a gradual onset (over months or years, not hours or days).
- History of worsening cognition (as observed by someone else).
- The most prominent cognitive deficit should be an impairment in learning and memory of recently learned information (plus evidence of dysfunction in at least one other cognitive area, as defined in the dementia section) or trouble finding words when talking; problems recognizing faces and objects and difficulty reading; or impaired reasoning, judgment and problem-solving, plus other cognitive problems.
Individuals who meet these criteria and have a genetic mutation that’s implicated in Alzheimer’s are even more likely to have the disease.
The workgroup also published guidelines for a diagnosis of possible Alzheimer’s dementia. The person must meet one of the following criteria:
- The person has the cognitive problems described in the clinical criteria for Alzheimer’s disease, but the symptoms came on suddenly; there’s a lack of historical information regarding symptoms; or there’s not enough objective documentation of progressive decline.
- The individual meets all of the clinical criteria for Alzheimer’s dementia but has one of the following: a history of stroke related to the onset or worsening of cognitive impairment; features of dementia with Lewy bodies; evidence of having another neurological disease; or medication use or a non-neurological condition that could affect cognition.
Home-screening tests for Alzheimer’s disease are available. However, the Alzheimer’s Association advises against using them because of their inability to predict who does not have dementia and the potential for psychological distress.
In the future, biomarkers (meaning biological markers, such as proteins in blood or spinal fluid, genetic mutations or brain changes that can be seen via imaging techniques) may play a greater role in an Alzheimer’s diagnosis.
Currently, they are being tested in research settings. The hope is that the illness could be diagnosed before symptoms start. Treatments could target the disease in its earliest stages-before brain damage or mental decline occur.
Two laboratory tests, called the ADmark Assays, can aid in the diagnosis of Alzheimer’s disease. One of these assays measures beta-amyloid and tau protein in the cerebrospinal fluid (and therefore requires a spinal tap). Its use is currently discouraged because its accuracy is equivalent to that of a careful clinical evaluation, which should be conducted anyway.
The second test identifies which variation of a protein called apolipoprotein E (APOE) the person carries. APOE is one of the lipoproteins that carry cholesterol and other fats in the blood. But the test is not definitive because some individuals with this allele will never develop Alzheimer’s. This test is not part of a routine evaluation of people with dementia.
Some people without dementia request testing for their APOE type, but this is discouraged for several reasons. First, the presence of an APOE allele indicates only that the person is at increased risk for developing Alzheimer’s disease, not that he or she will definitely develop it.
Second, a panel of experts assembled by the National Institutes of Health recommended against testing for the APOE gene because, at this point, no preventive treatment or cure is available for Alzheimer’s. Furthermore, awareness of the gene’s presence could cause the person unnecessary anxiety or lead to discrimination by employers or health insurance companies.
CT and MRI scans are used to examine brain structure and function and to rule out other possible causes of mental impairment. A CT scan uses an X-ray method that makes hundreds of images while rotating 360 degrees around the area that is being studied. A computer processes these images to produce two-dimensional cross-sectional images of the area-like slices from a loaf of bread.
This technique can identify some causes of dementia, such as stroke, brain tumor, brain abscess or hydrocephalus (fluid in the brain). While it can identify shrinkage of certain portions of the brain, which may suggest the presence of Alzheimer’s disease, many normal individuals also undergo a loss of brain volume as they age.
MRI can also detect some of the structural changes associated with Alzheimer’s disease. Like CT, MRI forms two-dimensional, cross-sectional images of the brain. But MRI relies on a powerful magnet rather than X-rays to capture the images. Because the technique is based on the amount of water in a given tissue, MRI provides a more refined and clearer view of the brain, and it exposes the patient to less radiation.
A promising development in imaging is a technique called functional MRI that looks not only at the structure of the brain but also at the metabolic processes taking place at the time of the scan. For example, functional MRI can detect changes in brain activity that occur as different areas of the brain are stimulated by tests of, say, memory or mathematical skills.
PET and SPECT imaging examine how the brain is working metabolically by determining how much of a radioactive tracer is taken up by brain cells. Two imaging agents, florbetapir F18 (Amyvid) and Pittsburgh Compound B (PIB), allow researchers to see the earliest deposits of amyloid plaque.
Another experimental imaging compound known as FDDNP reveals the presence of amyloid plaque and neurofibrillary tangles. All three agents are used with PET scans.
Functional MRI and PET with PIB or FDDNP may join Amyvid as approved tools for the detection of early signs of Alzheimer’s; however, the benefit of these tests is not yet proved and they are not routinely recommended.